Recently, there has been considerable interest within the detergent industry in liquid detergent compositions which are "concentrated" and, therefore, have low dosage volumes. Many attempts have been made to produce these concentrated products with less than about 50% water and higher active ingredient levels in the product. These low dosage, concentrated products are currently in high demand since they conserve resources and can be sold in smaller packages which are more convenient for consumers.
Moreover, liquid detergents containing anionic and nonionic surfactants, and capable of providing superior cleaning performance, are currently on the market. Some of these compositions contain alkyl polyethoxylate sulfate and/or polyhydroxy fatty acid amide surfactants to enhance removal of grease/oil stains. The stabilization of liquid detergent products containing high levels of these surfactants and other optional active ingredients and lower levels of water is particularly difficult because the hydroxyl and ethoxy groups of surfactants hydrogen bond with water molecules making them immobile.
Hydrotropes, including compounds such as sodium benzene sulfonate, sodium toluene sulfonate, sodium cumene sulfonate and sodium xylene sulfonate, are well known in the liquid detergent field particularly for their characteristic ability to increase the aqueous solubility of various slightly soluble organic chemicals. However, many of these compounds have been found to be ineffective in providing phase stability to concentrated heavy duty liquid detergent compositions containing anionic surfactant (including alkyl polyethoxylate sulfate surfactant) and polyhydroxy fatty acid amide surfactant.
Despite the fact that it is difficult to formulate a clear, homogeneous and phase stable liquid laundry detergent composition containing higher levels of anionic surfactant and polyhydroxy fatty acid amide surfactant and lower levels of water, it has been found that the phase stability of these detergent compositions is improved by utilizing water-soluble salts of toluene sulfonic acid in the liquid detergent compositions. Similar compositions containing other known hydrotropes, e.g., sodium cumene sulfonate and sodium xylene sulfonate, do not provide the requisite phase stability.